Polyester resins have enjoyed extensive use as coating materials for many substrates in recent years. The polyester resins are useful as they are capable of forming good hard films which are quite protective to the substrate on which they are used.
A major problem involving the use of polyester resin coatings had been the expense and time involved in curing the resins to a hard coating. The use of catalysts and heating in an oven is a slow and expensive process. Although the use of actinic light as a fast and inexpensive method of curing selected compositions became known, polyester resins could not be satisfactorily cured by actinic light in the presence of air. Thus the actinic light cure of polyester resins necessitated an enclosed atmosphere of inert gas such as nitrogen. Although the method was still faster than the catalytic cure, the necessity of the inert atmosphere is quite expensive.
It was found that the addition of wax to polyester resins would allow the resins to be cured by actinic light in the presence of air. This process was also a slow process, however, as the wax must be allowed to migrate to the surface during cure and the compositions respond very slowly to actinic light. Thus, slow line speeds had to be used.
It has now been discovered that wax-free polyester resin compositions may be admixed with an epoxy-based diacrylate to form a composition which cures rapidly when subjected to actinic light in the presence of air.
The polyester which is admixed with the diacrylate may be any unsaturated polyester.
The polyesters are ordinarily mixtures of a polyester of an alpha-beta ethylenically unsaturated polycarboxylic acid and a polyhydric alcohol.
The ethylenically unsaturated polycarboxylic acids include such acids as:
Maleic acid PA1 Fumaric acid PA1 Aconitic acid PA1 Mesaconic acid PA1 Citraconic acid PA1 Itaconic acid PA1 Dichloromaleic acid PA1 Ethylene glycol PA1 Diethylene glycol PA1 triethylene glycol PA1 polyethylene glycol PA1 propylene glycol PA1 dipropylene glycol PA1 polypropylene glycol PA1 glycerol PA1 neopentyl glycol PA1 pentaerythritol PA1 trimethylol propane PA1 trimethylol ethane PA1 succinic acid PA1 adipic acid PA1 suberic acid PA1 azelaic acid PA1 sebacic acid PA1 phthalic acid PA1 isophthalic acid PA1 terephthalic acid PA1 tetrachlorophthalic acid PA1 tetrabromophthalic acid PA1 styrene PA1 divinylbenzene PA1 methyl acrylate PA1 methyl methacrylate PA1 hexyl acrylate PA1 2-ethylhexyl acrylate PA1 octyl acrylate PA1 octyl methacrylate PA1 2-hydroxyethyl acrylate PA1 vinyl toluene PA1 p-tertiary butyl styrene PA1 ethylene glycol diacrylate PA1 vinyl acetate PA1 vinyl propionate PA1 vinyl benzoate PA1 allyl cyanide PA1 butyl vinyl ether PA1 cetyl vinyl ether PA1 diallylphthalate PA1 triallyl isocyanurate PA1 allyl acrylate PA1 2-methoxyethyl acrylate
And halo and alkyl derivatives of such acids and the like; the preferred acid being maleic acid. The anhydrides of these acids, where the anhydrides exist, are, of course, embraced under the term "acid", since the polyesters obtained therefrom are essentially the same whether the acid or anhydride is utilized in the reaction. The ethylenically unsaturated dicarboxylic acids are conventionally employed in an amount of about 10 mol percent to about 100 mol percent, although preferably in an amount of about 20 mol percent to about 80 mol percent of the total mols of acid component in the polyester.
The polyhydric alcohols useful in preparing unsaturated polyesters include:
and the like. The preferred polyols for the purposes of this invention have a molecular weight of less than about 2000 and consist essentially of carbon, hydrogen and oxygen. The polyhydric alcohols are generaly employed in an equal molar ratio to the total acid components, or as a slight excess, as, for example, about 10 mol percent excess.
Saturated dicarboxylic acids may be utilized in combination with the unsaturated acid or anhydride in the preparation of unsaturated polyesters. Such acids increase the length of the polyester without adding additional crosslinking sites, which is a desired feature in some polyesters. Examples of useful dicarboxylic acids which are either saturated or only aromatically unsaturated include:
and the like. As in the case of the ethylenically unsaturated acids, the anhydrides of these acids, where the anhydrides exit, are, of course, embraced in the term "acid", since the polyesters obtained therefrom are the same. Furthermore, the purposes of the present invention, the aromatic nuclei of such acids as phthalic acid are generally regarded as saturated since the double bonds do not react by addition, as do ethylenic groups. Therefore, wherever the term "saturated dicarboxylic acid" is utilized, it is to be understood that such term includes the aromatically unsaturated dicarboxylic acids. Such "saturated carboxylic acids" may also be referred to as "non-olefinically unsaturated" polycarboxylic acids.
A particularly preferred polyester is formed from a glycol and about 50 percent of an unsaturated acid and 50 percent of a saturated acid. An example is the polyester formed from neopentyl glycol and equimolar amounts of adipic acid and maleic anhydride.
To the polyester is added the reaction product of a member of the group consisting of acrylic acid and methacrylic acid with a polyglycidyl ether of a polyphenol or polyhydric alcohol.
The acid may be reacted with any polyglycidyl ether of a polyphenol or polyhydric alcohol. The preferred reactants are the polyglycidyl ether of a polyphenol such as Bisphenol A and acrylic acid. Other polyglycidyl ethers may be attained, for example, by etherification of a polyphenol with epichlorohydrin or dichlorohydrin in the presence of an alkali. The phenolic compound may be 2,2-bis(4-hydroxyphenyl) propane, 4,4'-dihydroxybenzophenone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxy-tertiarybutylphenyl)propane, bis(2-hydroxy-naphthyl) methane, 1,5-dihydroxynaphthalene, or the like. The polyphenol can also be a novolak resin or a similar polyphenol resin.
Such polyglycidyl ethers of polyphenols correspond to the average formula: ##EQU1## in which X represents an aromatic radical and z represents a whole or fractional small number.
Examples of this class of polyepoxides are the reaction products of Bisphenol A and epichlorohydrin, which correspond to the structure: ##SPC1##
in which z represents a whole or fractional small number.
Also suitable are the similar polyglycidyl ethers of polyhydric alcohols which may be derived from such polyhydric alcohols as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,4-butane diol, 1,5-pentanediol, 2,4,6-hexanetriol, glycerol, trimethylolpropane, and the like.
The acrylic or methacrylic acid and polyglycidyl ether are generally reacted in a temperature of from about 70.degree.C. to about 150.degree.C. and polymerization inhibitors such as di-tertiary butyl phenol, and the like, and catalysts such as quarternary ammonium salts, di-isobutyl cresoxy ethoxy ethyl dimethyl benzyl ammonium chloride, and the like, may be used in amounts of from about 0.1% to about 5%. Any molar ratio of acid to polyglycidyl ether may generally be used as the reaction is carried out stoichiometrically. However, the molar ratio of acid to polyglycidyl ether is generally about 2:1.
Vinyl monomers which crosslink with unsaturated polyesters to form thermosetting materials may be admixed with the acrylic compounds and polyesters, if desired. Such vinyl monomers may include:
and the like. The preferred vinyl monomers are liquid compounds, soluble in the polyester components. Such monomers should preferably be free of non-aromatic carbon-carbon conjugated double bonds.
The vinyl monomer as exemplified in the above lists may be employed over a broad range, but usually the proportion thereof, upon a weight basis, will be less than the polyester component. The amount of monomer should be sufficient to provide a liquid, flowable, interpolymerizable mixture. Ordinarily, the percentage of monomer will fall within the range of about 10 percent to about 60 percent by weight of the total mixture of polyester and monomer.
The amount of reaction product added to the polyester to achieve the final cure in air must be from about 10 percent to about 80 percent by weight of the polyester. At levels lower than about 10 percent, the mixture will not cure satisfactorily in the presence of air.
The vinyl aromatic content of the composition should preferably be less than 50 percent by weight based on the reactive components of the composition in order to more effectively use the lower levels of reaction product.
The coating compositions may contain photosensitizers to aid in the actinic light curing of the compositions. Various common photosensitizers are benzoin, benzoin methyl ether, diphenyl disulfide dibenzyl disulfide, benzil, benzophenone, xanthone, acetophenone, anthroquinone, and the like. Generally the coating may comprise from about 0.01 percent by weight of the photosensitizer to about 10 percent by weight of the photosensitizer.
The diacrylate and polyester and vinyl monomer (if desired) are merely mixed together to form the novel mixtures of this invention. If desired, the polyester may be heated slightly to facilitate the mixing.
The mixtures may be interpolymerized to form a film or coated onto a substrate and then interpolymerized. As these materials form strong and heat-resistant coatings, the use thereof is a preferred embodiment. The mixtures are interpolymerized by subjecting them to actinic light.
The composition comprising the diacrylate and polyester is cured into a hard, mar-free, generally stain resistant film by subjecting to actinic light. In general, the use of wave lengths in which sensitivity to actinic light occurs is approximately 1800 to 4000 Angstrom units. Various suitable sources of the actinic light are available in the art including by way of example, quartz mercury lamps, ultraviolet cored carbon arcs, and high-flash lamps.
The curing operation may take place in the presence of oxygen or air and no wax need be added to the polyester. The composition may be cured at line speeds of 50 feet per minute or greater and the films formed have improved hardness, stain resistance and abrasion resistance over films formed from the polyester alone.
The novel method of this invention may be used to coat substrates with polyester by merely applying the composition to the substrate and subjecting the composition to actinic light to cure in situ.
Any conventional means of applying the composition to the substrate may be used as dip coating, roll coating, spraying and the like.
The coated substrates are quite useful for plywood paneling, cabinets, furniture, printed paper products, cement, and cement asbestos products, and the like.